Electric furnace



Sepe 29, 1925 LSSSAQL c. A. CADWELL y ELECTRIC FURNACB Filed Nw. e, 19222 sheets-sheet 2 INVENTOR. Carfs CacZwe/ A TTORNEYS Patented Sept. 29,1925.

UNITED. STATES PATENT OFFlCE.

CHARLES L CASDWELL, F CLEVELAND, OEIS?, ASSIGNO '10 THE ELECTRIC RAILWAYIMPROVEMENT COMPANY, 0F CLEVELAND, OHIC, A. CORFORATICN 0F 01H10.

v Application led November 8, 1922. Serial, No. 599,641.

To all whom i may concer/n:

Be itknown that l, CHARLES A. CADWELL, a citizen of the United States,and a resident of Cleveland, county of Cuyahoga, and State of Ohio, haveinvented a new' and useful Improvement in Electric Furnaces, of whichthe following is a specification, the principle of the invention being`herein explained and the best mode in which I have contemplatedapplying that-principle, so as to distinguish lit from other inventions.

The present improvements relate more particularly to an electric furnaceof the oven type wherein a resistor -of granular material is employed,in conjunction with a plurality of electrodes so disposed relatively tosaid resistor that arcs are formed therebetween with resultantadditional heating effect.

Electric ovens for ordinary purposes are heated by passing an electriccurrent through metallic resistance paths, such as cast iron grids orvarious kinds of resistance wire. Such metallic resistance materialconstitutes in itself substantially all of the electrical equipmentneeded for any design of oven within the temperature range of suchmaterial, no auxiliar apparatus being required for control. owever, themaximum temperature of such an oven cannot be greater than that whichmay be derived by radiation from the metallic resistor at a safe Workingtemperature for the latter; although the maximum temperature thusderived' canvbe very nearly equal to such limiting temperature of theresistor, this being made possible by the uniformity of tem-- peratureof every part of the 4heating element and the easy distribution of theele-` ment itself.

Wherei-n order -to provide a higher temerature than can be obtained in'an oven lieated by such a metallic resistor, an electric arc or agranular resistor is employed, relatively elaborate and costlyelectrical equipment has heretofore been 'necessary for the operationand control ofthe furnace. Especially does such a'furnace lack theuniform distribution of heat V,energy characteristic of the metallicresistor'ovens,"being dependent rather upon radiation from sources ofextremely high heat intensity. such an arc of large currentcapacity orte resistance of a Y`large resistor body,y 1n' other words, where such aheating element is used, itis necessary to transform electric currentfrom the crdinary transmission lines by means of massive transformersand conductors into current of .very large amperage and lower voltage.Such an installation is necessarily costlyin litself and requires costlycontrol appah ratus.

Une object of the present invention, accordingly, is to provide an ovenor furnace wherein the temperature obtainable may far exceed the safelimit for metallic resistor ovens and yet `in which it is possible torealize the simplicity of construction, ease of control and small costof the latter. A further object is to render it possible to utilizecurrent taken directly from ordinary *transmission lines without anytransformation Whatever and with no more control apparatus than is usedin the metallic resistor type of oven.

he need for such an oven has long been felt for purposes that requirenot only a higher temperature than that obtainable from theaforesaidmetallic resistor type of oven, but also require a moreaccurate con-y trol of the rate and uniformity of heating and of 'thegases in the heating chamber,

than can be obtained from ordinary fuel fired furnaces.

For example, in the firing of fine pottery, a slow drying heat isrequired at the start and at' all times the Ware must be protectedagainst sudden changes of temperature which may occur in a fuel fired,furnace.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the means hereinafter fully desc ribedand particularlypointed out in the i claims, the annexed drawings and the followingdescription setting forth in detail certain mechanism embodying theinvention, such disclosed means constitu-ting, however, but one ofvarious mechanical forms in which the principle of the invention may beused.

Fig. 1 is a central vertical section of a furnace embodying my presentimprovements; Fig. 2 is a top plan View ofthe furnace proper with thecover removed and` other accessory parts `sectioned on the planeindicated by the line 2-2, Fig. 1;"Fig. 3 is a transverse horizontalsection of such furof a regular polygon in cross-section.

nace, the plane of the section being indicated by the line 3-3, Fig. 1;Fig. l is partly a plan view and partly a transverse horizontal sectionof certain auxiliary parts whereby the electrodes areadjustablysupported in the furnace, the plane of such section beingindicated by the line 4-4, Fig. 1; Fig. 5 is a more or less diagrammaticrepresentation of the wiring connections to the several electrodes; Fig.6 is a sectional view oit a detail of the apparatus accessory te thefurnace proper, the section being taken on the same plane as is Fig. lbut on a larger scale; and' Fig. 7 is a perspective view ot anotherdetail ot-such apparatus.

The oven or furnace chamber l, in the illustrative form shown in thedrawings`is primarily designed for tiring pottery or t'or heating other'articles of va similar character and requiring similar treatment. Suchchamber accordingly conveniently takes the form ot an approximatelycircular well sunl; practically Hush with the surface ot the surroundingHoor. l A refractory wall 2 oit lire-brick or like material, whiclr mayVbe backed with heat insulatingv material,

forms the outer confines of the chamber il, while an inner cylinder 3forms the lateral wall of the oven chamber proper.l Instead ot' the wellbeing circular and such wall 3 of cylindrical form, both may take theform Such inner wall 3 is preferably of carborundum or otequivalentrefractory material having a high heat conductivity and anelectrical resistivity that classes it as no more than a secondaryconductor. The purpose of this wall is that of a heat ditl'using anddistributing medium, as well as that of a container for an oven productthat requires a specified atmosphere; and where such oven product `is amelted metal, such inner wall .may take the form of a Crucible, i. e.,the cylinder will be closed at the bottom and so rendered capable ofbeing removed with the charge.

In any case'such inner chamber wall 3 rests on a layer 4 of granularcarbon or equivalent material that forms the' floor of the well," and asupplemental layer 5 of the same or similar material is placed' in `thebottom oit the annular space between walls 2 and 3. Embedded in suchlayer 4 is a series of resistor elements 6 (best shown in Figs. l and3), whichpreferably consist oit short pieces of cylindrical carbon rodspaced at short `intervals and laid transversely of such layer, i. e.,in a general radial direction with vrespect to lthe center The generalcon' of vthe furnace chamber. struction of the resistor forms thesubjectmatter of my co-pendinfrcapplication tiled April e9, 1920, serialo. 377,430, where such construction is broadly claimed.

Within the annular resistor space between walls 2 and 3 are suspended anumber of carbon electrodes 7 at regular intervals. In' the case of achamber having a polygonal cross-section, such electrodes will belocated at the spices of the polygon and on account of the general useot' -phase electric current, the number of such electrodes will usuallybe three for the smaller sizes of oven and some multiple of three forthe larger sizes observing only that any electrode on phase l, forexample, should be adjacent to phase 2 on one side and phase 3 on theother. Accordingly current flowing through adjacent electrodes and theportion of the resistor element consisting of the layer 5 and embeddedcarbon rods 6 lying between the lower ends of such electrodes, willencounter the resistance of suchl element and also that of two arcs.Aside from adding to the resistance ot the oven, these arcs also furnisha basis of control from an automatic variation of length, as will bepresently described.

The voltage ot the power line determines the length of the portion ofthe resistor element between adjacent electrodes and hence determinesthe number of the latter that can be used in a given sized unit. As ameans for increasing the length of the resistor element and Athereforeof the number of electrodes, without increasing the diameter of theannular resistor chamber, I may lace beneath each electrode, as shown inFigs. 1 and 3,' a cylindrical tile 8 of carborundum or equivalent'heatresistingl material and filled with granular carboni), such tile withits. Iilling resting upon the resistor element below and beingplacedwith its axis coincident with that of the electrode above. In thiscase the electrode will are to the top of such cylindrical tile into thegranular filling 9 and the radiating surface of the resistor element isthereby not only increased, but better heat distribution is secured dueto the vertical disposition of such added portion of the resistor.

Where the inner wall 3 of the oven is designed to remain permanently inplace, the annular resistor space or chamber between said wall and outerwall 2 will be closed at its upper end by blocks 10 of refractorymaterial, the inner edges of'which project a short distance beyond suchinner wall so as' to leave an opening through which access may be had tothe interior of the oven, as shown in Fig. 2. This opening is then inturn adapted to be closed by means of a cover 1'1, of similar refractorymaterial, that may be lifted or otherwise removed when access to theoven isl desired, `W here the inner wall 3 is in the form of a crucible,which requires to be lifted out of the furnace, the blocks 10 will, bfcourse, have to .llO

be supported with their inner edges clear of the upper end of such wall.It may also l be found desirablev to provide a second orv false bottom(not shown) within said] wall 3 which may be raised and lowered withl acharge, without disturbing the. disposalof 5 the apparatus located overthe oven' from which the electrodes 7 are suspended.

Certain of the blocks are provided with circular openings 12- fittedwith short' upwardly extending iron tubes 13 through 10 y which theelectrodes 7 are freely movable in a vertical direction, perforated,plates 14 of asbestos or the'like, fitting more tightly about theelectrodes, servingto close the upper ends or such .tubes 13..

The apparatus or mechanism from which the electrodes are thus suspendedcomprises a frame in the form of an open cage` 15 `which serves at thesame time as a base 'for the distribution of current to said electrodesand as anountingpor the control device with which each electrode isprovided. Said 'cage is itself suspended from a point overhead so aste-be vertically adjustable as a whole, a convenient n'ieansL for such isupport andadjustment comprising aV cable 16, onev end of which passesover a pulley 17 and is attached'to said cage, while the other end isconnected by means of a turn-l buclxle 18, or'like device, to a fixedpoint of A.30' support 19. Bly-the foregoing-means, the

cage with the electrodes suspended therefrom may be raised orlowered `soas to accurately vary the ar'c length of the electrodes as a unit.v Thecurrent -for theelectrodes is received at the upper end 'of the cage,`the three incoming conductors 2() where the current is B-phase, ashereinbefore assumed, be-

' ing cornlected to binding posts '21' corresponding in number tothenumber of electrodes, as shown in Fig. 5. From the distributing point atthe top of the cage pro-` vided by such binding posts, lengths /of bareHlexible conductors 22 -of nichrorne, or otherv non-corrosive ornon-oxidizing metal, ca-

v 4 5 pable of operating without injury at .a red eat, are stretchedvertically. to correspondving posts-23 at 4the lower end of the cage,

, a suitable length -or such .conductors being l three feet in the case"of a furnace such as illustrated. It will be understood, of course, thatthe binding posts 21 and 23 are suitably insulated from the cage so that-the current 7may pass through each such conductor 22 directly to thecorresponding ,electrode through a flexible copper conductor 24extending from such last-mentioned binding posts to the electrode holder2 5. Said holders 25 are vprovided with upwardly extending rods or stems26 that are received and adjustably held in tubular members 27, orrequivalent clamping devices, and the'latter are in turn supported fromthe cagel by means of cords 28 that pass over pulleys 29 mounted in saidcage and that have suitable 55 counterweghts 3Q attached at their innerends. It will be understood that the holders 25 are, of course,insulated from the supporting means thus provided and it should befurther explained that each counterweight 30 slightly overbalances thecorresponding electrode and other'parts attached to the outer end of itscord 28. The resultant tendency of v'the weight to raise the electrodeis,

however, restrained by a horizontall extending cord 31,the inner end ofwhichris attached, through the medium of an vinsulator 32, to anadjacent point on the corresponding nichrome conductor 22, `while theouter end passes around and is attached tothe periphery of a pulley 33,which pulley is fixed to the corresponding pulley 29 so that the twopulleys must always rotate together. As clearly shown in F ig. 1, thedirection in which each cord 31 thus passes around its correspondingpulley 83 is such as topull on the conductor 22, to which .said cord isattached at its inner end, yas on a bow string. The lengthening orshortening of `such conductor 22 will accordingly cause a rotation inone direction or the other of the attached pulleys 33 and 29, with theresult that the vertical position of the corresponding elect-rode willbe changed. For example, a current flow through any con-' ductor 22,which increases c the temperature of such conductor, will, by the sametoken,

increase its length and so allow the counterweight attached to thecorresponding electrode to raise the latter. As a result the Iarebetween such electrode and the resistor ing the ratio of the diametersof the pulleys 29and 33, as will be readily understood.

' In operating the oven the electrodes are first brought intocontact,withv the resistor element by lowering the cage as a whole and byadjustment of the clamp devices, including rod 26 and tube 27,` wherebythe individual electrodes are adjustably supported. Thereupon thecurrent is switched on and the electrodes, due to the lengthenin ofconductors 22, will immediately rise and start the arcs, following whichthe arcsare automatically maintained `at -the proper length by .thevaction of said conductors, as

has just been explained. f It' when thearcs are established and the ovenis running steadily it is desired to increase the lowof current and thusincrease the rate yof heating,

it is necessary only to slightly lower the cage and thus the electrodesas a whole; While to retard the rate of heating, the cage and electrodeswill be similarly raised.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being madeas regards the mechanismherein disclosed, provided the means stated by any of the followingclaims Ior the equivalent of such stated means be employedc I thereforeparticularly point out and. distinctly claim as my invention l. In anelectric furnace, the combination. of an approximately circular chamber;an annular resistor at one cud ofsaid chamber; and a series ofelectrodes extending into said chamber from the opposite end andapproximately parallel with the axis thereof to viithin arcing range ofsaid resistor,

2. In an electric furnace, the combination of an approximately circularchamber; an annular resistor at one end of said chainber; and a seriesof electrodes extending into said chamber from the opposite end andapproximately parallel with the yaxis thereof to Within arcing range ofsaid resistor7 said resistor being constructed so as to` provide a pathof least resistance for the current in passing from one ofsaidelectrodes to the other in a plane spaced from the adjacent end ofsaid chamben 3. In an electric furnace, the combination of anapproximately circular chamber; an annular resistor at one end of saidchamber; and a series of electrodes extending into said chamber from theopposite end thereof to Within arcing range of said resistor, saidresistor yconsisting of granular carbon and members of greaterelectrical conductivity embedded therein.

4L. In an electric furnace,y the combination of anapproximately circularchamber; an annular resistor at one end of said chamber; and a series ofelectrodes extending into said chamber from the opposite end thereof towithin arcing range of said resistor, said resister consisting of`granular carbon and a plurality of carbonrods embedded therein, anddisposed in a radial direction with respect to the axis of said chamber.,y

5. In an electric furnace, the combination of an approximately circularchamber; an annular resistor at one end of said chamber; and a series ofelectrodesextending into said chamber from the opposite end thereof toWithin arcing range of said resistor, said resister including elementsprojecting therefrom in line with said electrodes; respec tively.

6. In an electric furnace, the combination 0f an approximately circularchamber; a refractory Wall within said chamber spaced from the outerWall thereof; a resistor at one end of said chamber disposed in theannular space between such Walls; and a series of electrodes extendin tinto such space from the opposite end of geld chamber to 'Within arcingrange of said resistor.

L lin any electric furnace, the combination of an approximately circularchamber; a refractory Wall Within said chamber spaced from the outerWall thereof:I resistor at one end of said chamber disposed, in the annular space between such walls; and a series of electrodes en Lendinginto such space from the opposite end of said chamber to Within arcingrange of said resistor, said resistor being constructed so as to providea path of least resistance for the current in passing from one of saidelectrodes to the other yin a. plane spaced from the adjacent end 'ofsaid chamber.

8. In an electric furnace, the combination of an approximately circularchamber; a refractory Wall Within said chamber spaced from the outerWall thereof; a resistor at one end of said chamber disposed in theannular space between such Walls; and a series of electrodes extendinginto such space from the opposite end of said chamber 'to Within arcingrange of said resistor, said resistor including elements projecting therfrom in line with said electrodes, respectively.

9. In an electric furnace, the combination of a vertically disposed,approximately circular chamber; a refractory wall Within said chamberspaced from the outer Wall thereof; a resistor at the bottom of saidchamber disposed in the annular space between such walls; and a seriesof electrodes approximately parallel with the axis of said chamberdepending .vertically from above into such space to within arcingr rangeof said resistor.

l0. In an electric furnace, the combination of a vertically disposed;approximately circular chamber; a refractory Wall Within said. chamberspaced from the outer Wall thereof; a resistor at the bottom of saidchamber disposed in the annular space between such Walls; a series ofelectrodes depending vertically from above into such space to Withinarcingrange of said resistor; and means affected by the flow of currentto said electrodes adapted automati cally to raise and lower the sameindividuallyt ll. In an electric furnace, the combination of avertically disposed., approximately circular chamber; a refractory wallwithin said chamber spaced .from the outer Wall thereof; -a resistor atthe bottom of said chamber disposed in the annular space between suchWalls; a series of electrodes depending ,vertically from above into suchspace to Within arcing range of said resister; means adapted to raiseand lower said electrodes as a unit; and i'neans affected ltl l(it) bythe flow cf current to said electrodes adapted automatically to' raiseand lower the same individually..

l2. ln an electric -furnace, the combination of a vertically disposed,approximately circular chamber;a refractory wall within said chamberspaced from the outer wall thereof; a resistor at the bottom of saidfchamber disposed in the annular space between suoli walls; a series ofelectrodes decircular chamber; a refractory wall within.'

said chamber spaced from the outer wall thereof; a resistor at thebottom of said chamber disposed in the annular space between such walls;a series of electrodes depending vertically from above into such spaceto within arcing range of said resistor; means adapted to raise andlower said electrodes as a unit; manually adjustable means for raisingandlowering indi vidual electrodes; and means affected by the flow ofcurrent to said electrodes adapted automatically to raise and lower thesame individually.

14. 1in an electric furnace, the combination of a vertically disposed,approximately circular chamber; a refractory wall within said chamberspaced from the outer wall thereof; a resistor, at the bottom of saidchamber disposed in the annular space between such walls; a series ofelectrodes depending vertically from above 4 into. such space to Withinarcingrange of said resistor; conductors for supplying current to saidelectrodes, respectively, said conductors including sections secured topoints a predetermined distance apart; and means adapted automaticallyto raiseand lower said electrodes individually, said means beingaffected by variations in length of the corresponding conductor sectionsdue to changes in current flow therethrough.

15. in an electric furnace, the combination of a vertically disposed,approximately ci r cular chamber; a refractory wall within said chamberspaced from the outer wall thereof; a resistor at the bottom of saidchamber disposed in the annular space between such walls; a series ofelectrodes depending vertical-ly from above into such space to withinarcing range of said resistor; conductors for supplying current to said'electrodes, respective y, said conductors including sections secured topoints a predetermined dista ce aoart; means connected with indivi ualelectrodes tending to raise the same;

and connections between said means and the corresponding conductorsections, whereby vvariations inlengthof the latter serve to control'said means.

16. ln an electric furnace, the combination of a vertically disposed,approximately circular chamber; a refractory wall within said chamberspaced from the outer wall thereof; a resistor at the bottom of saidchamber disposed in the annular space lbe-v tween such walls; a seriesof electrodes depending vertically fom above' .into i such space towithin arcing range of said resistor; conductors for supplying currentto said electrodes, respectively, said conductors including sectionssecured to points a predetermined distance apart; a pulley adjacent eachsuch conductor section; a cable connected with the correspondingelectrode and passing` over such pulley, said cable beingcounter-weighted so as to tend t/o raise said electrode;-and a cordconnecting each p'ulley with the adjacent conductor section wherebytheshortening of the latter tends to lower saidelectrode.

17. In an electric furnace, the combination of a vertically disposed,approximately circular chamber; a refractory wall within said chamberspaced from the outer wall thereof; a resistor at the bottom of said Stichamber disposed in the annular space be tween such walls; a series ofelectrodes depending vertically from above into such space yto withinarcing range of said resister; conductors for supplying current to saidelectrodes, respectively, said conducf tors including sections securedto points predetermined distance apart; a pulley' ad jacent each suchconductor section; a cable adjustably connected with the correspcndingelectrode and passing over such pulley, said cable bein counter-weightedso as to tend to raise said electrode; and a cord connecting each pulleywith the adjacent conn ductor section whereby the shortening of thelatter tends to lower said electrode.

18. In an electric' furnace, the5 combination of a vertically disposed,approximately circular chamber; a refracto wall within said chamberspaced from tie outer wall thereof; a resistor at the Abottom of saidchamber disposed in the annular spaceA between such walls; a series ofelectrodes depending vertically vfrcc'ifi above into such spa/ce towithin arcing range of said resistor; a vertically adjustable frame oversaid chamber; conductors for su plying current to said electrodes,respective said conductors including sections secured to points 'on saidframe spaced a predetermined. distance apart; a ulley mounted in saidframe adjacent eac such conductor section; a cable adjustably connectedwith the corresponding .electrode and passing i wei hted so as to tendto raise said electro e; and a cord connecting each pulley with theadjacent conductor section whereby the shortening of the latter tends tolower said electrode.

19. In an electric furnace of the character described, the combinationwith a resistor and a series of electrodes movable towards and awaytherefrom; of conductors for supplying current to said electrodes,respectively, said conductors including sections secured to points apredetermined distance apart; and means adapted automatically to movesaid electrodes individually, said means being affected by variations inlen th of the corresponding conductor sections ue to changes in currentiiow therethrough.

20. In an electric furnace of the character described, the combinationVwith a resistor and a series of electrodes movable-towards and awaytherefrom; of conductors for supplying current to said electrodes,respectively, said conductors including sections secured to points apredetermined distance apart; means connected with individual electrodestending to move the same away from said resistor; and connectionsbetween said means and the corresponding conductor sections, wherebyvariations in length of the latter serve to control said means. f

Signed by me this 4th day of November, '1922.

CHARLES A. CADWELL.

